1. Field of the Invention
This disclosure relates to a sheet conveying apparatus conveying a sheet and an image forming apparatus.
2. Description of the Related Art
In the related art, an image forming apparatus such as a copier, a printer, or a facsimile includes a sheet conveying apparatus which conveys sheets. A sheet is conveyed to an image forming portion by the sheet conveying apparatus, and a toner image formed on a photoconductive drum is transferred onto the sheet. The sheet onto which the toner image has been transferred is conveyed to a fixing portion and is then conveyed to a discharging portion.
In a sheet conveying apparatus of the related art, when a sheet is conveyed, switching operations in various switching portions, switching operations of rotation directions in a sheet conveying portion, or the like are performed on the basis of detection of a front end of the sheet. A sheet detection portion which detects passage of the sheet is provided on a sheet conveying path in order to detect the front end of the sheet. By providing a plurality of sheet detection portions, it is possible to also detect, for example, conveyance delay or jamming of sheets.
Here, there is a sheet detection portion including a sensor flag (moving member) and an optical sensor. In such a sheet detection portion, if the sensor flag is pushed and rotated by a sheet and is thus moved to a detection position so as to be detected by the optical sensor, a control portion detects that the sheet has been conveyed on the basis of a signal from the optical sensor which detects the sensor flag. If a rear end of the sheet has passed through the sensor flag, the sensor flag is returned from the detection position to a standby position where the sensor flag can abut on a sheet to be conveyed, by a biasing force of a biasing portion. The sensor flag returned to the standby position abuts on a stopper portion so as to be positioned at the standby position.
However, when the sensor flag is positioned by the stopper portion, the sensor flag flips and causes chattering due to an impact when abutting on the stopper portion, and thus it takes a certain time for the sensor flag to be positioned at the standby position. For this reason, in the related art, as disclosed in JP-A-6-94444, for example, an impact absorbing material is provided on an abutting surface of the sensor flag abutting on the stopper portion, and thus the flipping of the sensor flag is minimized. As disclosed in JP-A-10-114446, an abutting surface of the sensor flag abutting on the stopper portion is tilted, and thus repulsive energy generated on the abutting surface is released in a thrust direction.
Meanwhile, in recent years, there has been a demand for improvement in the productivity, that is, improvement in the number of sheets on which images are formed in the image forming apparatus per unit time. For this reason, a sheet conveyance speed has been increased, or an interval (sheet interval) between a rear end of a sheet and a front end of the next sheet, the sheets being continuously conveyed, has been reduced. In order to reduce a sheet interval, in a sheet detection apparatus, the sensor flag is required to be returned to the standby position from the detection position in a short period of time after a preceding sheet passes.
Here, for example, if a biasing force of the biasing portion is increased, the sensor flag can be returned to the standby position in a short period of time. However, if a biasing force of the biasing portion is increased as mentioned above, an impact when abutting on the stopper portion is increased, and thus it takes time for the sensor flag to be positioned at the standby position, that is, the time required to be able to detect a distal edge of a sheet is lengthened.